1. Field of the Invention
The present invention relates to a motor drive control device and an image forming apparatus. More particularly, it relates to a control of rotationally driving a driven member in a predetermined state.
2. Description of the Related Art
Conventionally, in image forming apparatuses such as a copying machine and a printer, a high accuracy has been requested in a speed of a traction motor used for rotationally driving a photoconductive drum. Accordingly, a drum rotational speed outputted from an encoder mounted to a driving shaft of the photoconductive drum and a motor rotational speed outputted from an encoder mounted to an output shaft of a motor as a drive power source of the photoconductive drum are fed back, so that a speed control with respect to a traction motor is performed. Such rotational driving device has been proposed in, for example, Japanese Patent Unexamined Publication No. 2003-18880 (patent document 1).
However, a motor rotational speed outputted from an encoder mounted to an output shaft of the motor includes only an effect such as a torque ripple which occurs alone in a traction motor, and slipping and the like which occurs in a traction decelerator is disregarded. Therefore, it is difficult to accurately control a rotational speed of the motor to be a target speed. Further, the drum rotational speed outputted from the encoder mounted to the driving shaft of the photoconductive drum includes an effect such as a torque ripple which occurs alone in the traction motor and a non-linear element such as slipping which occurs in the traction decelerator. Accordingly, it is difficult to cancel those elements from the output by filtering and use the same, and a rotational speed control with respect to the photoconductive drum becomes unstable. Therefore, it is difficult to realize an accurate rotational speed control with the motor rotational speed control by merely feeding back the motor rotational speed and the drum rotational speed.
In the case of the rotational driving device shown in the patent document 1, the drum rotational speed is fed back, and amplification at a predetermined gain based on the difference with respect to the target speed is performed to perform a speed correction. After that, the motor rotational speed is further fed back to the corrected signal, and amplification at a predetermined gain based on the difference with respect to the target speed is performed, so that a final speed control signal to be outputted to a motor driver is generated. However, if the speed control signal is generated by the two-step correction in accordance with the feedbacks of the drum rotational speed and the motor rotational speed, oscillation is likely to occur, and the generated speed control signal is not stable, so that it is difficult to perform a rotational drive control with respect to the photoconductive drum stably.